ABSTRACT

Every living organism, ranging from microorganisms to plants or animals, is continuously exposed to assault by pathogens from the environment. Humans have an immune system for protection against pathogens, which recruits antibodies and killer cells to recognize and annihilate specific invaders, respectively. But these adaptive immune responses act only in higher vertebrates (Matsunaga and Rahman, 1998). In plants, innate immunity is a ubiquitous defense mechanism involving production of antimicrobial proteins and peptides in the host that does not possess the antigenrecognition specificity of antibodies (Boman, 1995). Nevertheless, since these peptides and proteins are products of transcription and translation of a single gene, they can be delivered soon after infection, with only a small input of energy and biomass. Although the innate immune response of plants has been considered as a primordial defense system, it can exhibit activity against a variety of microorganisms (Thomma et al., 1998).